Programmable interfaces for sustainable thin film applications

Abstract

Metal thin films on polymers serve a variety of applications in the packaging, flexible electronics, and space sector. Challenges include mechanical failure during use, material restrictions, and non-recyclability. In the Al-Polyimide (PI) system, favorable adhesive properties are attributed to an amorphous Al-O-C interlayer [1-3] (IL, 5 nm) between metal film and substrate. Through a combined atomic layer (ALD) and physical vapor deposition (PVD) setup, we are able to mimic interlayers over a wide thickness range to study their mechanical and interfacial benefits. Using this setup, Al thin films with different Al2O3 interlayer thicknesses were deposited on a polyimide substrate. These bi-layer samples were subjected to equi-biaxial tensile loading [4] and unloading with in-situ X-ray diffraction and electrical resistivity measurements at Synchrotron SOLEIL. The evolution of Al film stress, width of the Al diffraction peak and electrical resistivity as a function of the applied strain and IL thickness could be determined. The Al layer thickness and microstructure as well as crack density and spacing were investigated using TEM and SEM analysis. PVD film growth can be positively influenced by a preceding ALD step. All film systems with artificial ALD interlayers show reduced roughness and grain width in their PVD sputtered Al layers, resulting in a higher 0.2% yield stress. This is possibly due to the ALD step modifying the PI substrate surface.